Several enzymes and proteins are involved with the replication of DNA. At a specific point, the double helix of DNA is caused to unwind possibly in response to an initial synthesis of a short RNA strand using the enzyme helicase. Proteins are available to hold the unwound DNA strands in position. Each strand of DNA then serves as a template to guide the synthesis of its complementary strand of DNA. DNA polymerase III is used to join the appropriate nucleotide units together.

A mutation is a change in the letters (DNA sequence) that make up a gene. This is sometimes referred to as a “spelling” mistake.

Genetic diseases can be inherited because they are mutations in the germ cells of the body—the cells involved in passing genetic information from parents to offspring. Genetic diseases can also result from changes in DNA in somatic cells, or cells in the body that are not germ cells.